1. Field of the Invention
The present invention relates to novel aqueous emulsions of organopolysiloxane compositions capable of being crosslinked in thin layers by hydrosilylation, and to the use of such emulsions for coating supple or flexible materials such as textile fibers, paper, board members, plastic substrates, metal sheets, and the like, particularly in order to render these materials water-repellant and/or nonadhesive as regards sticky substances.
2. Description of the Prior Art
Compositions of the above basic type have long been known to the silicone industry and are described individually in a great many patents and patent applications.
They comprise crosslinking systems of the same type, namely:
(i) at least one organopolysiloxane containing at least two vinyl groups per molecule, each bonded to a silicon atom, and designated hereinafter as the "SiVi" group;
(ii) at least one organohydropolysiloxane containing at least three hydrogen atoms per molecule, each bonded to a silicon atom, designated hereinafter as the "SiH" group; and
(iii) a catalytically effective amount of a platinum group metal compound for catalyzing the hydrosilylation reaction.
Thus, the use of a polyaddition aqueous emulsion to impart nonadhesiveness to paper is described in U.S. Pat. No. 3,527,659 (column 1, lines 25 to 28; column 2, lines 37 to 46; and column 3, lines 60 to 65).
The polyaddition aqueous emulsions in general, the inhibitory function of the platinum catalyst which is served by water and the production of a hardened composition on a substrate after the evaporation of water are described, furthermore, in the left-hand column on page 5 of French Pat. No. 1,528,464, corresponding to U.S. Pat. No. 3,445,420.
In the aforementioned passage, emphasis is placed on the fact that this formation of an aqueous emulsion can take place only under the conditions such that hydrolysis of the SiH groups occurs to but a minor extent.
U.S. Pat. No. 3,900,617 describes an aqueous emulsion comprising, as the vinylated diorganopolysiloxane, a diorganopolysiloxane blocked by a dimethylvinylsiloxyl group at both ends of the polymer. This patent also indicates that, in order to store the emulsion after its production, it is desirable to prepare two separate emulsions, one, designated component A hereinafter, comprising the vinylated diorganopolysiloxane and the hydrosilylation catalyst, and the other, designated component B hereinafter, comprising the hydrogenated diorganopolysiloxane.
The emulsifiers which can be employed are, in particular, polyvinyl alcohol in the case of component A and polyalkylene glycol ethyl ethers or alkylphenyl ethers in the case of component B.
French Pat. No. 2,338,316 also teaches that the emulsion should be stored as two separate components A and B, which are admixed on an ad hoc basic at the point in time of ultimate use and additionally stipulates that during the preparation of component A the platinum catalyst should be incorporated in the vinylated diorganopolysiloxane before it is emulsified.
Marketing in the form of these two components A and B such as described in the above two patents is not without disadvantages.
In the first place, the amount of water to be conveyed is large, and this increases transportation costs. Furthermore, and above all, the user must mix the quantities of components A and B before each use in well-determined proportions in order to provide both the required SiH/SiVi ratio and the amount of platinum catalyst.
It would be much more convenient for the user to have available an aqueous emulsion packaged as two components, the first component A comprising the polysiloxane containing SiVi and the polysiloxane containing SiH as an aqueous emulsion, preferably concentrated and extremely stable in storage and, as a second component B, an aqueous catalyzing emulsion of the hydrosilylation catalyst. In order to prepare the final composition, the user would then only have to dilute, if desired, a certain quantity of component A and to then add just the necessary amount of catalyzing emulsion of component B, and this would make it possible to eliminate possible risks of errors in the SiH/SiVi ratio and the amount of catalyst.